This disclosure relates generally to energy absorbing structures, particularly energy absorbers used in vehicle bumper systems.
Energy absorbing systems broadly find application in many situations where excess energy needs to be managed, without causing damage to surrounding objects. For example, in the automotive industry, such systems are also referred to as Energy Absorbers (EA) and find application in bumper systems of cars and the like.
Typically, bumpers are designed to absorb most of the impact in case of collisions with other objects, including vehicles, stationary objects or pedestrians, to minimize damage. The energy absorbers used in bumpers need to absorb the energy of low speed collisions to minimize vehicle damage and preserve vehicle safety, yet minimize the damage to pedestrians in low speed collisions as well. Varying performance requirements have been established by organizations such as the National Highway Traffic Safety Administration (NHTSA), Insurance Institute for Highway Safety (IIHS), and the Research Council for Automobile Repairs (RCAR). Other standards include the United States Federal Motor Vehicle Safety Standard and the Canada Motor Vehicle Safety Standard.
To meet today's rigorous safety standards while satisfying the requirements of current vehicle styling trends there exists a need for energy absorbing systems which are lightweight, cost effective, perform in small and large package space situations equally, and require minimum tooling expenses that meet both low volume and high volume build requirements. In general, there exists a need for energy absorbing systems capable of absorbing more energy at a lower mass, both within automotive applications and non-automotive applications.
A bumper system generally includes a beam that extends widthwise across the front or rear of a vehicle and is mounted to rails that extend in a lengthwise direction. The beam typically is made of steel or another rigid material, and the beam is stiff and provides structural strength and support.
The efficiency of an energy absorbing bumper system, or assembly, is defined as the amount of energy absorbed over distance, or the amount of energy absorbed over load. A high efficiency bumper system absorbs more energy over a shorter distance than a low energy absorber. High efficiency is achieved by building load quickly to just under the rail load limit and maintaining that load constant until the impact energy has been dissipated.
Foam energy absorbers have been used. However, foam based energy absorbers typically have slow loading upon impact, which results in a high displacement. This can be undesirable due to vehicle styling trends such as “low-offset bumpers” which minimize the amount of displacement available to the bumper system. Further, foams are effective to a sixty or seventy percent compression, and beyond that point, foams become incompressible so that the impact energy is not fully absorbed. The remaining impact energy is absorbed through deformation of the beam and/or vehicle structure.
It would be desirable to provide a bumper system or assembly which can meet required safety standards, is lightweight, reduces package space between the beam and fascia, and can minimize damage to both vehicle and pedestrian in vehicle-pedestrian collisions.